Java Doc for ByteBuffer.java in  » 6.0-JDK-Modules » j2me » java » nio » Java Source Code / Java DocumentationJava Source Code and Java Documentation

This class is provided as part of the JSR 239 NIO Buffer building block. It is a subset of the java.nio.ByteBuffer class in Java(TM) Standard Edition version 1.4.2. Differences are noted in bold italic. The class documentation may make reference to classes that are not present in the building block.

I/O channels, marking and resetting, and read-only buffers are not supported. Allocation of non-direct byte buffers, compaction, and duplication are not supported. The char, long, and double datatypes are not supported. The following methods are omitted:

• ByteBuffer allocate(int capacity)
• ByteBuffer compact()
• ByteBuffer duplicate()
• Buffer mark()
• Buffer reset()
• boolean isReadOnly()
• ByteBuffer asReadOnlyBuffer()
• CharBuffer asCharBuffer()
• LongBuffer asLongBuffer()
• DoubleBuffer asDoubleBuffer()
• char getChar()
• char getChar(int index)
• long getLong()
• long getLong(int index)
• double getDouble()
• double getDouble(int index)
• ByteBuffer putChar(char value)
• ByteBuffer putChar(int index, char value)
• ByteBuffer putLong(int index, long value)
• ByteBuffer putLong(long value)
• ByteBuffer putDouble(double value)
• ByteBuffer putDouble(int index, double value)

This class defines six categories of operations upon byte buffers:

• Absolute and relative get and put methods that read and write single bytes;

• Relative bulk get methods that transfer contiguous sequences of bytes from this buffer into an array;

• Relative bulk put methods that transfer contiguous sequences of bytes from a byte array or some other byte buffer into this buffer;

• Absolute and relative get and put methods that read and write values of other primitive types, translating them to and from sequences of bytes in a particular byte order; JSR 239 does not support certain multi-byte get and put methods.

• Methods for creating view buffers, which allow a byte buffer to be viewed as a buffer containing values of some other primitive type; and

• Methods for compacting, duplicating, and slicing a byte buffer. JSR 239 does not support compacting and duplicating buffers.

Byte buffers can be created either by allocation, which allocates space for the buffer's content, or by wrapping an existing byte array into a buffer.

Direct vs. non-direct buffers

A direct byte buffer may be created by invoking the allocateDirect factory method of this class. The buffers returned by this method typically have somewhat higher allocation and deallocation costs than non-direct buffers. The contents of direct buffers may reside outside of the normal garbage-collected heap, and so their impact upon the memory footprint of an application might not be obvious. It is therefore recommended that direct buffers be allocated primarily for large, long-lived buffers that are subject to the underlying system's native I/O operations. In general it is best to allocate direct buffers only when they yield a measureable gain in program performance. Certain JSR 239 methods require the use of direct buffers. JSR 239 does not support the techniques described in the remainder of this paragraph.

A direct byte buffer may also be created by mapping a region of a file directly into memory. An implementation of the Java platform may optionally support the creation of direct byte buffers from native code via JNI. If an instance of one of these kinds of buffers refers to an inaccessible region of memory then an attempt to access that region will not change the buffer's content and will cause an unspecified exception to be thrown either at the time of the access or at some later time.

Whether a byte buffer is direct or non-direct may be determined by invoking its isDirect method. This method is provided so that explicit buffer management can be done in performance-critical code.

Access to binary data

 float  getFloat()
 float  getFloat(int index)
 void  putFloat(float f)
 void  putFloat(int index, float f)

Corresponding methods are defined for the types char, short, int, long, and double. JSR 239 does not define the char, long, or double methods. The index parameters of the absolute get and put methods are in terms of bytes rather than of the type being read or written.

For access to homogeneous binary data, that is, sequences of values of the same type, this class defines methods that can create views of a given byte buffer. A view buffer is simply another buffer whose content is backed by the byte buffer. Changes to the byte buffer's content will be visible in the view buffer, and vice versa; the two buffers' position, limit, and mark values are independent. The asFloatBuffer method, for example, creates an instance of the FloatBuffer class that is backed by the byte buffer upon which the method is invoked. Corresponding view-creation methods are defined for the types char, short, int, long, and double. JSR 239 does not define views of type char, long, or double.

View buffers have three important advantages over the families of type-specific get and put methods described above:

• A view buffer is indexed not in terms of bytes but rather in terms of the type-specific size of its values;

• A view buffer provides relative bulk get and put methods that can transfer contiguous sequences of values between a buffer and an array or some other buffer of the same type; and

• A view buffer is potentially much more efficient because it will be direct if, and only if, its backing byte buffer is direct.

The byte order of a view buffer is fixed to be that of its byte buffer at the time that the view is created.

Invocation chaining

Methods in this class that do not otherwise have a value to return are specified to return the buffer upon which they are invoked. This allows method invocations to be chained.

The sequence of statements

 bb.putInt(0xCAFEBABE);
 bb.putShort(3);
 bb.putShort(45);
 

 bb.putInt(0xCAFEBABE).putShort(3).putShort(45);
 

The new buffer's position will be zero, its limit will be its capacity, and its mark will be undefined.

Modifications to this buffer's content will cause the returned array's content to be modified, and vice versa.

Invoke the ByteBuffer.hasArray hasArray method before invoking this method in order to ensure that this buffer has an accessible backing array.

If this buffer is backed by an array then buffer position p corresponds to array index p + arrayOffset().

Invoke the ByteBuffer.hasArray hasArray method before invoking this method in order to ensure that this buffer has an accessible backing array.

The content of the new buffer will start at this buffer's current position.

The content of the new buffer will start at this buffer's current position.

The content of the new buffer will start at this buffer's current position.

Two byte buffers are equal if, and only if,

1. They have the same element type,

2. They have the same number of remaining elements, and

3. The two sequences of remaining elements, considered independently of their starting positions, are pointwise equal.

A byte buffer is not equal to any other type of object.

This method transfers bytes from this buffer into the given destination array.

This method transfers bytes from this buffer into the given destination array.

Reads the next four bytes at this buffer's current position, composing them into a float value according to the current byte order, and then increments the position by four.

Reads four bytes at the given index, composing them into a float value according to the current byte order.

Reads the next four bytes at this buffer's current position, composing them into an int value according to the current byte order, and then increments the position by four.

Reads four bytes at the given index, composing them into a int value according to the current byte order.

Reads the next two bytes at this buffer's current position, composing them into a short value according to the current byte order, and then increments the position by two.

Reads two bytes at the given index, composing them into a short value according to the current byte order.

If this method returns true then the ByteBuffer.array() array and ByteBuffer.arrayOffset() arrayOffset methods may safely be invoked.

The hash code of a byte buffer depends only upon its remaining elements; that is, upon the elements from position() up to, and including, the element at limit() - 1.

Because buffer hash codes are content-dependent, it is inadvisable to use buffers as keys in hash maps or similar data structures unless it is known that their contents will not change.

Writes the given byte into this buffer at the current position, and then increments the position.

Writes the given byte into this buffer at the given index.

This method transfers the bytes remaining in the given source buffer into this buffer.

This method transfers bytes into this buffer from the given source array.

This method transfers the entire content of the given source byte array into this buffer.

Writes four bytes containing the given float value, in the current byte order, into this buffer at the current position, and then increments the position by four.

Writes four bytes containing the given float value, in the current byte order, into this buffer at the given index.

Writes four bytes containing the given int value, in the current byte order, into this buffer at the current position, and then increments the position by four.

Writes four bytes containing the given int value, in the current byte order, into this buffer at the given index.

Writes two bytes containing the given short value, in the current byte order, into this buffer at the current position, and then increments the position by two.

Writes two bytes containing the given short value, in the current byte order, into this buffer at the given index.

The content of the new buffer will start at this buffer's current position.

The new buffer will be backed by the the given byte array; that is, modifications to the buffer will cause the array to be modified and vice versa.

The new buffer will be backed by the the given byte array; that is, modifications to the buffer will cause the array to be modified and vice versa.

The new buffer's position will be zero, its limit will be its capacity, and its mark will be undefined. Whether or not it has a backing array is unspecified. For JSR 239, the mark is undefined, and no backing array will be present..
Parameters:
  capacity - The new buffer's capacity, in bytes. The new byte buffer.
throws:
  IllegalArgumentException - If the capacity isa negative integer.

Modifications to this buffer's content will cause the returned array's content to be modified, and vice versa.

Invoke the ByteBuffer.hasArray hasArray method before invoking this method in order to ensure that this buffer has an accessible backing array.

If this buffer is backed by an array then buffer position p corresponds to array index p + arrayOffset().

Invoke the ByteBuffer.hasArray hasArray method before invoking this method in order to ensure that this buffer has an accessible backing array.

The content of the new buffer will start at this buffer's current position. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent. JSR 239 does not support the mark.

The new buffer's position will be zero, its capacity and its limit will be the number of bytes remaining in this buffer divided by four, and its mark will be undefined. The new buffer will be direct if, and only if, this buffer is direct, and it will be read-only if, and only if, this buffer is read-only. JSR 239 does not support the mark or read-only buffers. A new float buffer.

The content of the new buffer will start at this buffer's current position. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent. JSR 239 does not support the mark.

The new buffer's position will be zero, its capacity and its limit will be the number of bytes remaining in this buffer divided by four, and its mark will be undefined. The new buffer will be direct if, and only if, this buffer is direct, and it will be read-only if, and only if, this buffer is read-only. JSR 239 does not support the mark or read-only buffers. A new int buffer.

The content of the new buffer will start at this buffer's current position. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent. JSR 239 does not support the mark.

The new buffer's position will be zero, its capacity and its limit will be the number of bytes remaining in this buffer divided by two, and its mark will be undefined. The new buffer will be direct if, and only if, this buffer is direct, and it will be read-only if, and only if, this buffer is read-only. JSR 239 does not support the mark or read-only buffers. A new short buffer.

Two byte buffers are compared by comparing their sequences of remaining elements lexicographically, without regard to the starting position of each sequence within its corresponding buffer.

A byte buffer is not comparable to any other type of object. A negative integer, zero, or a positive integer as this bufferis less than, equal to, or greater than the given buffer.
throws:
  ClassCastException - If the argument is not a byte buffer.

Two byte buffers are equal if, and only if,

1. They have the same element type,

2. They have the same number of remaining elements, and

3. The two sequences of remaining elements, considered independently of their starting positions, are pointwise equal.

A byte buffer is not equal to any other type of object.

This method transfers bytes from this buffer into the given destination array. If there are fewer bytes remaining in the buffer than are required to satisfy the request, that is, if length > remaining(), then no bytes are transferred and a BufferUnderflowException is thrown.

Otherwise, this method copies length bytes from this buffer into the given array, starting at the current position of this buffer and at the given offset in the array. The position of this buffer is then incremented by length.

In other words, an invocation of this method of the form src.get(dst, off, len) has exactly the same effect as the loop

 for (int i = off; i < off + len; i++)
 dst[i] = src.get(); 

This method transfers bytes from this buffer into the given destination array. An invocation of this method of the form src.get(a) behaves in exactly the same way as the invocation

 src.get(a, 0, a.length) 

Reads the next four bytes at this buffer's current position, composing them into a float value according to the current byte order, and then increments the position by four.

Reads four bytes at the given index, composing them into a float value according to the current byte order.

Reads the next four bytes at this buffer's current position, composing them into an int value according to the current byte order, and then increments the position by four.

Reads four bytes at the given index, composing them into a int value according to the current byte order.

Reads the next two bytes at this buffer's current position, composing them into a short value according to the current byte order, and then increments the position by two.

Reads two bytes at the given index, composing them into a short value according to the current byte order.

If this method returns true then the ByteBuffer.array() array and ByteBuffer.arrayOffset() arrayOffset methods may safely be invoked.

The hash code of a byte buffer depends only upon its remaining elements; that is, upon the elements from position() up to, and including, the element at limit() - 1.

Because buffer hash codes are content-dependent, it is inadvisable to use buffers as keys in hash maps or similar data structures unless it is known that their contents will not change.

Writes the given byte into this buffer at the current position, and then increments the position.

Writes the given byte into this buffer at the given index.

This method transfers the bytes remaining in the given source buffer into this buffer. If there are more bytes remaining in the source buffer than in this buffer, that is, if src.remaining() > remaining(), then no bytes are transferred and a BufferOverflowException is thrown.

Otherwise, this method copies n = src.remaining() bytes from the given buffer into this buffer, starting at each buffer's current position. The positions of both buffers are then incremented by n.

In other words, an invocation of this method of the form dst.put(src) has exactly the same effect as the loop

 while (src.hasRemaining())
 dst.put(src.get()); 

This method transfers bytes into this buffer from the given source array. If there are more bytes to be copied from the array than remain in this buffer, that is, if length > remaining(), then no bytes are transferred and a BufferOverflowException is thrown.

Otherwise, this method copies length bytes from the given array into this buffer, starting at the given offset in the array and at the current position of this buffer. The position of this buffer is then incremented by length.

In other words, an invocation of this method of the form dst.put(src, off, len) has exactly the same effect as the loop

 for (int i = off; i < off + len; i++)
 dst.put(a[i]); 

This method transfers the entire content of the given source byte array into this buffer. An invocation of this method of the form dst.put(a) behaves in exactly the same way as the invocation

 dst.put(a, 0, a.length) 

Writes four bytes containing the given float value, in the current byte order, into this buffer at the current position, and then increments the position by four.

Writes four bytes containing the given float value, in the current byte order, into this buffer at the given index.

Writes four bytes containing the given int value, in the current byte order, into this buffer at the current position, and then increments the position by four.

Writes four bytes containing the given int value, in the current byte order, into this buffer at the given index.

Writes two bytes containing the given short value, in the current byte order, into this buffer at the current position, and then increments the position by two.

Writes two bytes containing the given short value, in the current byte order, into this buffer at the given index.

The content of the new buffer will start at this buffer's current position. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent. JSR 239 does not support the mark.

The new buffer's position will be zero, its capacity and its limit will be the number of bytes remaining in this buffer, and its mark will be undefined. The new buffer will be direct if, and only if, this buffer is direct, and it will be read-only if, and only if, this buffer is read-only. JSR 239 does not support the mark or read-only buffers.

The new buffer will be backed by the the given byte array; that is, modifications to the buffer will cause the array to be modified and vice versa. The new buffer's capacity will be array.length, its position will be offset, its limit will be offset + length, and its mark will be undefined. Its backing array will be the given array, and its array offset will be zero.

The new buffer will be backed by the the given byte array; that is, modifications to the buffer will cause the array to be modified and vice versa. The new buffer's capacity and limit will be array.length, its position will be zero, and its mark will be undefined. Its backing array will be the given array, and its array offset will be zero.